Because this faction does not leave the Black Pyramid Settlement, they will recruit armies and park them there. This makes conquering them difficult, as after some time they may have two or three full armies plus the garrison outside their walls. Enemy factions also do not understand the value of disbanding units and recruiting higher tier ones, so the stacks mostly be Skeleton Warriors and Skeleton Spearmen. This can honestly lead to some of the more fun battle in a campaign as its hordes upon hordes of skeletons with some more decent units in the garrison. Regardless, one should only attack this faction if they want to conquer their one settlement, and should be prepared for a challenging fight if they are unprepared. Of course, this can be used as an opportunity to farm these enemies through lighting strikes, though this should be done if the army you send in has high tier units.